Typically, a cultivator driver wishes to drive between the rows of plants, such as immature soybean plants, but the driver cannot see individual plants or even identify the rows very well because they are obscured by weeds. When the driver can see the plants, the fatigue of doing so is very great after a few hours. This invention is useful to survey crop rows and to provide fine steering corrections so that the vehicle stays centered when driving between rows.
It is necessary to position the blades of a cultivator so they are centered exactly midway between the crop rows. The allowable margin of error consists of only the width of the soil between the rows which is not occupied by the roots of the crop. Because the spread of the roots is approximately equal to the canopy width of the crop, the farmer uses the crop's canopy as a visual guide to steer the machine. As the crop matures and the roots spread, the margin for error is reduced until an accuracy of only a few inches remains, and steering mistakes cause crops to be damaged or weeds to be missed.
For these reasons various mechanical means to assist row guidance have been developed. Past practice includes a heavy metal ball which is dragged between the rows. In ridge-tilled crops, the ball rolls to the low point between rows which tends to be midway between rows. A mechanical arm that is attached to the ball operates a hydraulic valve which sends steering corrections to the cultivator to keep it centered between the rows. This device works well when rows are well defined. When they are not, it is inaccurate. At its worst, it can skip to the next row and it can also be upset by weeds.
Another practice uses mechanical wands which sense the distance to the crop's stalks on either side of the device. It is frequently used on corn crops which have well defined stalks. This device, however, tends to give false readings when in contact with weeds.
An acoustical range sensor device is sometimes used. This sensor also tracks the mid-point between single rows but, because it contacts only one point of the soil surface at a time, it can be confused by weeds or other irregularities in the soil surface. Its main advantage is that it cannot become entangled in weeds.